1. Field of the Invention
This invention relates to lightweight construction blocks with central voids for the reception of reinforced concrete, and more particularly to such blocks formed of a composite of materials and to methods of making these blocks.
2. Prior Art
Extensive development efforts have been directed toward forming construction blocks of foamed plastic which have central voids adapted to receive concrete slurry. The blocks act as forms for molding the load supporting reinforced concrete frame, and remain in place to provide the finished wall surfaces, insulation and vapor barrier. The foamed plastic does not act as a load bearing member in the finished structure but simply acts to retain the concrete slurry in the form during the hardening process. The light weight of the plastic allows these blocks to be made in relatively large modules, i.e., eight feet high and eight feet wide, and yet to be handled manually, without any special materials handling equipment. The blocks are typically formed with interlocking configurations on their edges so that a plurality of blocks may be stacked relative to one another with their voids aligned to form continuous channels for the reception of concrete slurry.
It has been proposed that these blocks be formed of polyurethane, polystyrene, or other foamed plastic materials. One of the most important obstacles to the wide-spread use of these blocks in construction has derived from the fact that all of these organic materials decompose to varying extents depending on the formulation under sufficient heat, sometimes generating noxious gases, and some may additionally tend to support combustion to a degree.
Certain forms of porous inorganic materials exist, such as stranded fiberglass mats and "FOAMGLAS", a product made by baking a slurried glass grit with a gas releasing reactor, which do not decompose to any appreciable extent under heat, nor support combustion, and it has been proposed that the lightweight block forms for reinforced concrete construction be formed of these materials. Blocks formed primarily of these inorganic materials do improve the fire resistance of a structure relative to the resistance of a structure formed of foamed plastic blocks, but they create several new problems. First, the inert materials have substantially higher thermal conductivity than the foamed plastic materials and accordingly the resultant structures are not nearly as well insulated, per relative unit thickness of material. Second, the inorganic foam materials in general, and those based on glass in particular, are very brittle and may easily break in transit or when subjected to the forces created during vibration of the concrete slurry. Additionally, the inorganic foams are not self-foaming and are much more difficult and expensive to mold than the foamed plastics and are much heavier as well.